Operators drill wells many thousands of feet in the search for hydrocarbons. The wells are expensive and take a significant amount of time to plan. To obtain hydrocarbons such as oil and gas, boreholes are drilled by rotating a drill bit attached to a drill string. The drill bit is typically mounted on the lower end of the drill string as part of a bottom-hole assembly (BHA) and is rotated by rotating the drill string at the surface and/or by actuation of down-hole motors or turbines.
Operators find it important to obtain data about the various subterranean reservoirs once the actual drilling begins. Thus, measurement while drilling (MWD) tools have been developed that gather information about the subterranean reservoirs and telemetry the data to the surface. A variety of sensors employed in the drill string are used to monitor various down-hole conditions, such as pressure, spatial orientation, temperature, or gamma ray count, that are encountered while drilling. Engineers and geologist can then use this data in an effort to understand the formations and make plans on completion, sidetracking, abandoning, further drilling, etc.
The use of sensors during the drilling operation to provide information related to positioning or steering the drill, such as direction, orientation and drill bit information, is referred to as “Measurement While Drilling” (MWD). The phrase “Logging While Drilling” (LWD) is often used to using sensors for petrophysical or geological measurements during drilling. As used herein, “MWD” will also be used to encompass LWD applications unless otherwise specified.
Most of the existing MWD systems were developed for drilling directional wells through clastic or carbonate reservoirs and are not well suited for drilling unconventional drilling programs, which are typically characterized by long, deviated laterals and which require advanced hydraulic fracturing for production. The problems with existing MWD systems are associated with measurement accuracy, measurement type, BHA incompatibility, and cost-effectiveness.
What is needed is an improved MWD system specifically designed for geosteering in unconventional wells.
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